The present invention relates generally to the field of hydraulic circuits utilized in automatic transmission systems and, more particularly, to a direct replacement valve mechanism for a 1-2 Shift Valve that regulates hydraulic fluid pressure within the valve body to affect proper shifting of the transmission from first to second gear.
Automatic transmission systems of the prior art have a hydraulic circuit sub-system which includes at least a hydraulic pump, a valve body having fluid conducting passages or circuits, input and exhaust ports formed within the fluid circuits, and a plurality of spool valves so-called because of their resemblance to sewing thread type spools. Such valves are comprised of cylindrical pistons having a plurality of piston lands formed thereon, which alternately open and close the ports to regulate the flow and pressure of automatic transmission fluid (hereinafter xe2x80x9cATFxe2x80x9d) within the hydraulic circuits to actuate different components of the transmission. It will be understood that in describing such hydraulic circuits, ATF usually changes names when it passes through an orifice or control valve in a specific circuit.
The so-called 1-2 Shift Valve regulates proper gear shifting from first to second gear in automatic transmissions such as the General Motors 4T60E transmission and other similar automatic transmissions made available on General Motors vehicles. The original equipment manufacture (hereinafter xe2x80x9cOEMxe2x80x9d) 1-2 Shift Valve on such transmissions is fabricated from a low grade aluminum material, which is subject to premature wear and scoring. Further, the OEM valve also has a large reaction area and is highly affected by side loading (i.e. vertical movement) caused by ATF entering the valve under pressure, which wears the mating bore prematurely.
As the wear increases the OEM valve tends to stick and/or eventually seize in the bore during its reciprocating movement from the first gear to the second gear position due to mechanical friction between the worn surfaces of the valve piston and the mating bore. This produces a characteristic shift problem in the General Motors 4T60E transmission wherein the second gear clutch slips or xe2x80x9cshuddersxe2x80x9d and may completely prevent a shift to second gear.
Thus, the present invention has been developed to resolve this problem and other shortcomings of the prior art.
The theory of forces exerted upon a hydraulic piston by fluid flowing past it has been the subject of considerable scholarly study, which has been applied to practical valve piston construction in the prior art. One example of such a study appears in the article, xe2x80x9cContributions to Hydraulic Controlxe2x80x9d by Lee and Blackburn, Transactions of the ASME, August, 1952, in which a theory is given of the origin of the steady-state force exerted upon a piston by fluid flowing past its corner. In this article reference is made to a considerable body of experimental evidence in support of that theory.
Another such example is disclosed in the article, xe2x80x9cCFD Simulation of Steady-State Flow Forces on Spool-Type Hydraulic Valvesxe2x80x9d by Miller et al., Society of Automotive Engineers, 1999, which describes a new methodology for determining the steady-state flow force on a hydraulic flow valve.
However, these prior art references do not teach or suggest the combination of structural features and functional aspects of the present invention.
Accordingly, the present invention is a direct replacement 1-2 Shift Valve for the GM 4T60E transmission, which restores a smooth 1-2 gear shift thereby correcting the xe2x80x9cshudderxe2x80x9d shift or complete failure to shift from first to second gear, which is a common service complaint among owners of a vehicle with this transmission.
The present 1-2 Shift Valve includes at least one bi-directionally tapered valve stem having fluid deflecting and/or redirecting surfaces that change the direction of transmission fluid flow upon ingress of fluid into the valve such that a rebound force is generated by the fluid""s impact with the defelecting surfaces, which acts to propel the valve piston in an axial direction to facilitate the shift from first to second gear.
In addition, the so-called spools or piston lands, which comprise the valve piston are provided with a plurality of annular grooves that function to retain a layer of ATF bout the circumference of the valve piston to buffer it against side loading (i.e. lateral movement) within the mating bore during operation. Further, the present valve piston is provided in an anodized aluminum finish, which reduces surface friction and increases service longevity.
Other features and technical advantages of the present invention will become apparent from a study of the following description and the accompanying drawings.